Motors which advance rotationally or linearly in discrete increments of motion are commonly used for exact positioning of a movable part such as the paper chart of a recorder, a dispersing element in a monochromator, a variable control device or any instrumental or mechanical element whose position must be settable by some electrical means. A motor which can be so advanced or stepped is commonly known as a stepper motor. Such motors combine a variety of electrical and mechanical elements, often in quite a small volume. They may be stepped in either direction by switching electrical excitation from one set of actuating windings to another in alternating sequence; each switch operation causing the rotor to advance one step and hold in the new position. By repeating the switching operation alternately a specific number of times or counts a specific change in position will be effected in the position of the motor's armature.
It is common to continue to excite a stepper motor after a predetermined number of counts is completed and the motor is at rest. This holds the motor or "detents" it in its final step position. However, this practice has a disadvantage in that stepper motors are not very efficient at rest and dissipate considerable heat. This can be objectionable where the space available for the motor is confined as, for instance, where the motor is used to drive a recorder chart. It is also objectionable where a number of motors are required for multiple functions or where heat buildup may adversely affect operation of the controlled device.
It is an objective of our invention to provide stepper motor driving means controlled by a microprocessor through software that will have sharply reduced heat dissipation during non-stepping periods.
It is further an objective to retain in this stepper motor driving means the same positioning accuracy as is provided by conventional driving means.
It is another objective to minimize the power supply requirements in multiple motor systems by making possible a common power supply which handles all motors, one motor at a time, without curtailing motor usage or accuracy.